1. Field of the Invention
The present invention generally relates to an apparatus and a method for transmitting/receiving data in a High Rate Packet Data (HRPD) system, and more particularly to a transmission/reception apparatus and method for supporting an Orthogonal Frequency Division Multiplexing (OFDM) scheme and a Multiple Input Multiple Output (MIMO) technology as well as an Evolution Data Only (EV-DO) transmission scheme in an HRPD system.
2. Description of the Related Art
With rapid development of communication technology, current mobile communication systems are providing not only ordinary voice communication services but also high rate data services which enable transmission of large-capacity digital data, such as moving images, as well as transmission of an e-mail or a still image, by using a Mobile Station (MS).
Representative examples of mobile communication systems currently providing high rate data services include an EV-DO system, an OFDM system, etc. An EV-DO system uses one of the high rate data service standards proposed by the Qualcomm company of the United States for transmission of large-capacity digital data and has been one-step evolved from a conventional Code Division Multiple Access (CDMA) 2000 1× in order to provide a forward transmission speed of 2.4 Mbps. An EV-DO system is also called an “HRPD system.”
Further, one of representative wireless communication systems employing a multi-carrier transmission scheme is an OFDM system. According to an OFDM scheme, a serial symbol sequence is converted into parallel symbol sequences and the parallel symbol sequences are modulated with a plurality of mutually orthogonal sub-carriers before being transmitted. OFDM schemes have come into the spotlight since the beginning of the 1990's according to development of Very Large Scale Integration (VLSI) technology.
According to an OFDM transmission scheme, data is modulated with multiple sub-carriers, and the sub-carriers maintain orthogonality between them. Therefore, an OFDM transmission scheme is stronger against a frequency selective multi-path fading channel and is more proper for HRPD services, such as a broadcasting service, than a conventional single carrier modulation scheme.
A slot structure and a transmitter structure in a forward link of a typical HRPD system will now be briefly described.
A forward link of an HRPD system uses a Time Division Multiple Access (TDMA) technology for multiple access, and uses a Time Division Multiplexing (TDM)/Code Division Multiplexing (CDM) scheme for multiplexing.
FIG. 1 shows a slot structure of a forward link in a conventional HRPD system. One slot has a structure including repeated one-half slots. Each of the one-half slots includes a pilot signal 103 or 108 having an Npilot chip length, which is inserted at a center thereof and is used in channel estimation of the forward link in a receiver of an MS. Medium Access Control (MAC) signals 102, 104, 107, and 109, each of which has an NMAC chip length and includes reverse power control information and resource allocation information, are located at both sides of associated pilot signals 103 and 108. Further, actual transmission data 101, 105, 106, and 110, each of which has an NData chip length, are located at opposite outer sides of associated MAC signals 102, 104, 107, and 109. In an HRPD system as described above, a slot of a forward link has been multiplexed according to a TDM scheme in which a pilot, MAC information, data, etc. are transmitted at different time points. In the slot structure shown in FIG. 1, the MAC information and the data are multiplexed according to a CDM scheme using Walsh codes, and the pilot signal, the MAC signal, and a small block unit of data have been set to have sizes such that Npilot=96 chips, NMAC=64 chips, and NData=400 chips, respectively, in the forward link of the HRPD system.
FIG. 2 shows a transmitter of a conventional HRPD system. Packet data of a data channel passes through a channel encoder 201 for channel-encoding the packet data, a channel interleaver 202 for interleaving the encoded data, and a modulator 203 for modulating the interleaved packet data. Data of a MAC channel passes through a channel encoder 204. The pilot tone, the MAC signal, and the data pass through a TDM multiplexer (MUX) 206 and then form a physical link having a slot structure of FIG. 1. The data output from the TDM MUX 206 is transmitted to users through an antenna (not shown) after passing through a sub-carrier modulator 207. Reference numeral 208 in FIG. 2 denotes an HRPD processor for compatibility with an HRPD system, which includes the channel encoder 204, the TDM MUX 206, and the sub-carrier modulator 207.
However, an HRPD system having the above-described structure is insufficient for adequate support of wideband data transmission and efficient use of frequency resources, which are used by next generation systems, such as broadcasting service systems. In order to support wideband data transmission and efficient use of frequency resources, a need exists to provide a solution for high speed data transmission and efficient use of frequency resources by using multiple antennas and a proper data modulation scheme.